How to get a single uv island
Preferably I would do this by setting custom seams and unwrap it from a certain viewport (orthograpgic camera top - left etc 5 on numpad and then the voewport of your choice). 
If you have a seameless tiled texture instead, you may just want to avoid uv mapping completely or use it afterwards to bake your textures on your model, which means that you will be in need of a very nice and well unfolded pelt.
So, if you tend to follow the second method (since you have one seamless texture) use the mapping node in your material node editor and in case you insist for a quick unwrap, use unwrap from viewport w